The present disclosure relates to high intensity electric discharge lamps. It finds particular application in those instances where the lamp is subject to uncontrolled increases and decreases in wattage and therefore temperature over a short period of time, which can result in lamp failure due to failure of weld joints and other sensitive features under such power cycling circumstances. However, it is to be appreciated that the present disclosure will have wide application throughout the lighting industry.
Lamps for which the present disclosure may prove suitable include any lamp characterized by the inclusion of a discharge envelope of fused silica containing a discharge-supporting filling of gas or vapor, for example. The lamp usually includes at least one pair of electrodes with gap>3 mm between which an electric discharge passes in operation of the lamp. An electric current is supplied to the electrodes from a source exterior to the lamp envelope via what is commonly called a ribbon seal. This seal generally comprises a strip of refractory metal foil, commonly of molybdenum, having one end thereof electrically connected to a respective electrode, and the opposite end in electrical contact with a refractory metal rod which passes through the end wall of the envelope to provide an external lead. The foil, electrodes, and lead rods are embedded in the fused silica envelope wall.
In order to stabilize the foil-electrode-lead rod assembly during manufacture and use, it has been suggested that portions of the assembly be wrapped in a coil of refractory metal wire, such as for instance tungsten. The assembly passes through a segment of the envelope which is pinched during manufacture to provide support for the assembly. However, during fusing of the pinched silica portion of the envelope, it is difficult to maintain the integrity of the assembly without damaging the foil, electrodes and/or lead rods. The addition of a coil provides a means to strengthen the assembly and to absorb some of the heat generated during fusing of the envelope, because the fused silica can collapse around the coil during the pinching process without jeopardizing directly the assembly components.
While the foregoing coil, which is set forth completely in U.S. Pat. No. 4,550,269, to our common assignee, achieves the goal of providing support for the assembly and dissipating some heat, a continuing problem remains with regard to integrity of the assembly during repeated power cycling at levels above and below those for which the lamp is stabilized. This can occur in some electric systems which are not well regulated for total wattage or energy supply. A certain consequence to the lamp of experiencing this type of power cycling and temperature fluctuation is degradation of the welds applied to connect the assembly components, which then necessarily leads to lamp failure as the connections are compromised.
The invention disclosed herein is intended to provide a lamp assembly which addresses the foregoing concerns by providing a connector to improve the connection between any one lead and the foil. The connector contemplated herein, due to its configuration, allows an increased surface area at the point of contact between the lead and the foil, thus strengthening the weld at that point. The connector further provides a means for dissipating heat and energy build up at the weld joint. This results in improved thermal and electrical performance of the lamp, regardless of cycling of the exterior power source, or other difficult operational parameters.